Nutritive Value of Raw and Heated Casein With and Without Added Amino-acids

Abstract

Experiments previously reported 1 have shown a loss in nutritive value of wheat gluten and casein when these proteins had been exposed to a temperature of 150 C. for 30 minutes. In an attempt to determine the site of injury to the protein molecule thus indicated new experiments have been made using supplements of various amino-acids to the diets containing raw and heated casein.

The casein in the present series was heated uniformly at 140°C. in a thin layer for 30 minutes. The growth of young rats fed diets containing various levels of the raw and heated casein as sole sources of protein and the nitrogen balance or biological value of such diets for mature rats were used as criteria of the nutritive efficiency of the proteins. These procedures were then repeated, the diets being supplemented with various amino-acids. The methods are described in a former publication. 1

Results of Growth Experiments. Young rats fed for 28 days from weaning diets containing raw and heated casein at 9, 12, 15, 18, and 22% levels grew better in all cases on the raw casein. Eight to 16 rats were used for each diet tested. The food intakes were quite similar but the resulting growth was in all cases less when the heated casein was used. The gain in weight per gram of protein eaten was greatest at the 12% level for both raw and heated casein and decreased slightly with each increase in level. However, the difference between the two types of diet, raw and heated, remained nearly the same, 0.20 to 0.34, at all levels, the values being 2.10 to 1.61 for the raw, and 1.76 to 1.40 for the heated diet.

The 12 and 15% raw and heated casein diets were then fed, supplemented by 0.2% lysine, histidine, tyrosine, cystine and tryptophane respectively.